1. Field of the Invention
The present invention relates to puffer type circuit breakers, and in particular to such circuit breakers having a gaseous arc-extinguishing medium and which generate a blast of arc-extinguishing gas towards the contact area of the circuit breaker.
2. Prior Art
In circuit breakers of the so-called puffer-type, the gas blast energy is generated by compression of gas in a cylinder during the breaking operation. In order for such a breaker to manage a given interruption involving a certain current at a certain recovery voltage, two conditions have to be fulfilled at the zero current passage in question:
(a) The contact distance shall exceed a certain minimum value;
(b) The blast pressure in the cylinder shall exceed a certain minimum value.
Since the phase position of the current may vary arbitrarily, the extinguishing interval of the breaker must be sufficiently long, that is, the breaker shall fulfil conditions (a) and (b) for a sufficiently long time, 12-18 milliseconds (condition c).
In a conventional puffer type circuit breaker, the movable contact normally has to perform about two-thirds of its stroke before conditions (a) and (b) are fulfilled. When endeavouring to make such a breaker more rapid, one will soom come into conflict with condition c, that is, the demand for a sufficiently long extinguishing interval, since the pump means consisting of the piston and the cylinder reaches its end position too soon and the blast pressure disappears. For this reason, conventional puffer type circuit breakers will probably not reach shorter breaking times than 2 cycles (i.e. 33 milliseconds in a 60 Hz system).
In a proposed puffer-type circuit breaker as described in German Auslegeschrift No. 1,966,973, a movable bridging contact, which is joined to the puffer cylinder, connects two nozzle contacts, one of which is fixed and the other is movable and joined to the puffer piston. During the first part of the breaking operation, the movable nozzle contact is moved towards the fixed nozzle contact, and the speed at which the contact distance initially increases is determined solely by the movement of the bridging contact.